Method of forging and lubricant therefor



Nov. 4, 1947.

Filed Jan. 27, 1944 FIG. 1. -7

I /4 l4 4 5 L :FIG. 4; [3

FIG. 5.

Danald WShern-zan INVENTOR.

BY $4M ATTORNEti Patented Nov. 4, 1947 UNI-TED STATES PATENT OFFICE METHOD OF FORGING AND LUBRICANT THEREFOR Application January 27, 1944, Serial No. 519,940

15 Claims. 1

This invention relates to a method of forging and lubricant therefor.

The principal object of the invention is to re duce the pressure required in performing a given forging operation and correlatively to increase the amount of metal flow that can be obtained with a single stroke of a forging press.

Another object of the invention is to enable the production in a single forging operation of articles that heretofore required many forging operations and in some instances could not be forged at all.

Another object is to provide a method of forging utilizing temperatures approaching the melting point of the blank to thereby make the metal flow easier and obtain a greater flow in a single forging operation.

Another object is to provide a novel lubricant for the dies capable of use at high forging temperatures and of reducing the pressure required for a given forging operation.

Another object is to prevent excessive cooling of the metal being forged by the dies.

Another object is to provide a method of forging very thin pieces of large surface area from heavy billets.

Other objects will appear hereinafter.

The accompanying drawings illustrate the application of the invention to the forging of thin sheets of large surface area'with a patterned surface from cylindrical or other shaped symmetrical bar stock.

In the drawings:

Figure 1 is a perspective view of a bar from which the stock is made showing diagrammatically the preferred method of heating the same by electric resistance heating;

Fig. 2 is a perspective view of a lower die with its lubricant coating;

Fig.3 is a transverse section showing the forging dies separated and with the bar in location therebetween;

Fig. 4 is a similar section showing the dies midway of the forging operation; and

"Fig. 5 is a perspective view of the finished forged article.

The invention arises from the desire to manufacture a plate I of the shape illustrated in Fig. 5, and having a longitudinal central rib 2 and a plurality of spaced transverse ribs 3 at' thin sections have a tendency to lose their heat quickly in processes where reheating and successive forging is employed.

The invention is based on the discovery that by employing a proper lubricant and by uniformly heating a symmetrically shaped steel bar 4 to a very high temperature, just under the melting temperature of the metal, where its resistance to flow is at a minimum, and then quickly transferring the bar to the forging dies and applying the latter, the finished plate I can be forged in a single operation without having to exert forces exceeding the resistance of the dies to crushing load and without the attendant defects caused by nonuniform heating in prior attempts to forge the plate.

In carrying out the invention the bar 4 is pref erably of cylindrical shape, since this shape lends itself to uniform heat radiation and to a reasonably uniform rate of heating. The bar is preferably coated with a spray 5 of a ceramic enameling material which melts and fuses during heating of the bar and protects the same from scale at the high temperatures employed.

The heating of the bar 4 is preferably carried out immediately adjacent or in the forging press by means of the two electrodes 6 and I pressed into. contact with the opposite ends of the bar. The electrodes 6 and 1 are connected by leads 8 and switch 9 to a suitable source in of heating current. The heating current is allowed to flow endwise through the bar 4 until the latter is heated to above 2400" R, which is just under the melting temperature of the steel employed. The heated bar is then dropped into the press il in the position illustrated in Fig. 3.

In preparation for the forging operation the dies I2 and I3 of the press II are first coated with a ceramic enameling material and fired to fuse and bond the material to provide a coating l4 of ceramic enamel over the entire active surface of the dies. The enamel employed is preferably of a hard type with good wetting properties and fired at about 1600 F.

Before the forging operation, the dies are preferably preheated to about 600 F. to reduce the temperature differential between the dies and the bar 4.

In'the forging operation the ceramic enamel serves as a lubricant for the dies and tends to prevent undesirable heat loss from the bar 4 being formed. The enamel 5 that is on the bar 4 is already molten prior to starting the forging operation. 'I'he enamel M which is on the dies is hard and solid. As the bar 4 engages the enamel l4, the heat of the bar instantaneously melts the portion of the enamel so engaged, and as the forging operation continues and the metal of the bar 4 flows outwardly in the flattening of the bar and contacts more of the enamel l4, the latter melts and has a tendency to run ahead of the flowing metal as illustrated in Fig. 4 at [5. However, the bonding of the enamel to the surface of the dies insures that the enamel will be largely retained over the entire surface during the forging operation.

After each forging operation the dies are cleaned and re-enameled for another use. There should be a number of sets of dies on hand so that the press can be kept in operation. In some instances it is possible to fuse the enamel to a die lining which may be used over again a number of times or thrown away and replaced with a new lining after each forging operation. Various dies are illustrated in applicants copending application, Serial No. 519,939, filed on even date herewith and issued to Patent No. 2,384,349 on September 4, 1945.

The ceramic enamel composition employed may be varied without loss of the results. The higher the melting point of the enamel, the more effective it is in retaining its position between the blank being forged and the dies, and in preventing loss of heat from the blank. A glass enamel composition having higher fusion points than that described for the enamel may be of advantage for some forging operations. On the other hand, the lower fusion point enamels are better for lower temperature forging operations.

The spread between the firing temperature of the enamel and the forging temperature of the blank should be sufficiently large to assure that the enamel will be of reasonably low viscosity at all points of contact with the flowing metal. If the shape of the article being forged and the heating of the blank are insufficient to maintain the flowing metal at the last stages of forging at a temperature above the firing temperature of the enamel, the latter may remain solid and prevent a satisfactory forging.

The thickness of the enamel [4 will depend upon many factors. The enamel on the die surface hould be above ten thousandths of an inch thick and satisfactory results on the forging described have been obtained with a two-coat enamel somewhat thicker. The enamel 5 applied to the bar 4 may be thinner and a single coat has been found satisfactory where the die faces were also enameled.

Without the enamel as a lubricant it was found that the flowing metal of the blank was cooled so rapidly by the dies that it froze or became rigid before the plate had been completely formed, and the resistance to forming required pressures in excess of the crushing strength of the dies. Attempts were made with a forging force of 1,800 tons without success on the particular piece being forged. When using the enamel lubricant, it was found that the complete piece could be forged with a single stroke of the press and employing less than 200 tons force.

The enameling material 5 on the bar 4 is also effective as a lubricant and in the forging of some articles it may besuilicient to enamel the forging blank only, leaving the die without enamel. This is generally cheaper and may be effective -where lower forging temperatures are employed, just above the melting point of the enamel, and where the length of the flow is small so that the enamel is not scraped off in the forging operation. With the plate I illustrated, however, it was found that greatly improved results could be obtained by enameling the working faces of the dies. The high forging temperature required to obtain the large fiow of metal had a tendency to free the enamel on the bar from its bond with the metal, and a uniform coating of the required thickness on the bar could not be assured. Furthermore, the greatly extended surface of the final plate I as compared to that of the bar 4 resulted in a rupture of the enamel coating on the bar in attempting to spread itself.

These difficulties are not present when the dies are enameled. The enamel l4 on the dies is in a solid state and bonded to the metal die surface when the forging operation starts. As the bar 4 engages the enamel, the latter is melted by the heat of the bar, and the progressive melting of more enamel as the bar flows out between the dies serves to provide a constant supply of molten lubricant at the place most needed. There is no requirement that the enamel spread over a larger area as the forging operation progresses and there is always a fresh supply of enamel of given amount present at the crucial point of advance flow of the forging metal.

Various embodiments of the invention may be employed within the scope of the accompanying claims.

The invention is claimed as follows:

1. A method of forging comprising heating the work piece to be forged, and applying dies thereto under pressure to form the same in the presence of a ceramic enamel die lubricant.

2. In hot metal working, the employment of a lubricant composed of molten ceramic enameling material of good wetting properties and melting below the temperatures employed in the hot metal working to reduce the friction and heat losses.

3. A method of forging comprising applying and firing a ceramic enamel coating on the working face of a forging die, heating the blank to be forged to a. temperature substantially in excess of the firing temperature of the enamel, and applying the die to the heated blank to forge the same.

4. A method of forging comprising applying a ceramic enameling material to coat the blank to be forged, heating the blank to a forging temperature above the firing temperature of said material, and forging the blank when so heated.

5. The method of forging comprising applying and firing a ceramic enamel coating on the working face of a forging die, applying a ceramic enameling material to coat the blank to be forged, heating the blank to a temperature substantially above the temperature at which the enamel was fired on the dies, and applying the die to the heated blank to forge the same.

6. A method of decreasing the friction between a heated metal work piece and a die in forging operations, comprising supplying a ceramic enamel between the die and the flowing metal of the work piece.

'I. The method of decreasing the loss of heat from a heated metal blank being forged to the forging die, comprising supplying a ceramic enamel between the die and the metal of the blank.

8. A die lubricant for forging operations comprising a ceramic enameling material of good wetting properties and fired around 1600 F.

9. A die lubricant for forging metal comprising a. coating of ceramic enameling material on the surface of the blank being forged of good wetting properties and flowing below the forging temperature employed,

10. A die lubricant for forging metal at high temperatures, comprising a refractory material melting at a temperature substantially below the forging temperature and having good wetting properties.

11. The method of forging a product having at least a. portion thereof of substantial surface area and very thin, presenting difficulties in maintaining the required forging temperature in the blank, comprising employing a relatively thick blank heated uniformly to a high forging temperature and forging the product therefrom with a single stroke of a forging press in the presence of a ceramic enamel die lubricant.

12. The method of forging a product having at least a portion thereof of substantial surface area and very thin, presenting difllculties in maintaining the required forging temperature in the blank, comprising employing a relatively thick blank heated uniformly to a high forging temperature and forging the product therefrom with a single stroke of a forging press while supplying molten refractory lubricant thereto.

13. The method of forging a product having at least a portion thereof of substantial surface area and very thin, presenting difllculties in maintaining the required forging temperature in the blank, comprising employing a relatively thick blank of symmetrical section, coating the blank lubricant, heating the blank to a high forging temperature in position between the dies of a forging press, the heating operation serving to fuse the refractory material and thereby protect the surface of the blank from scaling, and immediately thereafter forging the blank to produce the product in a single stroke of the press.

14. The method of forging a product having at least a portion thereof of substantial surface area and very thin, presenting difllculties in maintaining the required forging temperature in the blank, comprising employing a relatively thick blank of symmetrical section, heating the blank to a high forging temperature in position between the dies of a forging press, and immediately thereafter forging the blank to produce the product in a single stroke of the press while supplying a ceramic lubricant thereto.

15. In hot metal working, the lubrication of the workpiece by a molten glass like refractory material of good wetting properties and melting below the temperatures employed in the hot metal working.

DONALD W. SHERMAN.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,112,779 Forsyth Oct. 6, 1914' 1,692,488 Dannell Nov. 20, 1928 1,693,130 Anderson Nov. 27, 1928 2,089,030 Krathy Aug. 3, 1937 Clausen Oct. 31, 1939 

